Four principal types of electroceramics are dielectrics, piezoelectrics, electrooptic and optical materials. Such electroceramics are used in such devices as capacitors, sensors, transducers, actuators, waveguides, and optical storage media. Barium titanate, often with additives such as liquid-phase sintering aids, grain growth inhibitors, stabilizers, and curie-point shifters, is a common material used for ceramic capacitors. Piezoelectric, electro-optic and optical devices are commonly made of lead zirconate titanate (often referred to as "PZT") or lanthanum-modified PZT (often referred to as "PLZT"), and other dopants or additives may be added to either system. Other previously used electroceramic compositions include bismuth titanate, lead niobate, sodium potassium niobate, lead titanate and other compounds including elements from columns IV-A and V-A of the periodic table.
The common method for producing ceramic oxide bodies involves blending the ceramic precursor (oxide, carbonate, etc.) powder with one or more of a solvent, dispersant, plasticizer and binder, forming a green body by tape casting or extrusion, and firing the green body so as to pyrolize the organic components, form the desired phases, and densify the body. A wide range of such compositions and the prior art methods by which they are prepared are discussed in some detail in Ceramic Materials For Electronics Processing, Properties and Applications, edited by Relva C. Buchanan and published by Marcel Dekker, Inc. of New York and Basel in 1986.
The different prior art processes are subject to various limitations. While the use of organic additions has aided in the shaping of green bodies, difficulties encountered during organic pyrolysis (e.g., non-uniform shrinkage, incomplete burnout, formation of stable carbonates) can make formation of dense, complex shapes with a desired microstructure difficult. In particular, there is needed a procedure which can be used to form non-planar geometries and constructions, e.g., coaxial or multi-layer bodies, or curved beam devices, and which can be used to make multi-layer capacitors and similar structures in which the individual ceramic layers are less than 20 microns (and preferably less than 10 micron) thick.
U.S. Pat. No. 4,826,808, which is also here incorporated by reference, discloses a method of producing a composite of superconducting oxide by first forming a precursor alloy which includes the metallic elements of the desired superconducting oxide and then oxidizing the alloy to form the complex superconducting oxide. The patent discloses mixing at least one "noble" metal element (e.g., a metal whose oxide is thermodynamically unstable under the reaction conditions employed) with the alloy elements, and then oxidizing the alloy-noble metal elements to form a structure in which a substantially pure noble metal phase is intimately mixed with the superconducting oxide.